DANDONG, China, April 12 (Reuters) - A single, ancient-looking North Korean helicopter dropped five paratroopers on their side of the Chinese border on Friday in a rather less-than-defiant, lonely show of force following weeks of angry war rhetoric from Pyongyang.
North Korea has ramped up its threats after being hit by new U.N. sanctions since carrying out a third nuclear test in February, prompting the United States to fly stealth jets over the peninsula and to prepare anti-missile systems for Guam and Alaska.
U.S. and South Korean officials say they have detected no signs of a military build-up in North Korea, whose vast armed forces are in any case believed largely to be poorly equipped and poorly trained, though a formidable array of missiles and artillery is aimed at South Korea.
A Reuters reporter in the Chinese city of Dandong, which borders the reclusive state, said he could see North Korean paratroopers dropping from a Soviet-era helicopter during a drill above Sinuiju, which lies opposite Dandong.
Five people jumped from the helicopter into the hazy skies and pulled their parachutes before the aircraft flew low and disappeared behind the tree line across the Yalu River that divides the two countries.
There was no sign of other military activity.
Six equally ancient bombers could be seen sitting quietly beside the runway of Sinuiju's airfield.
Further down, where the border crosses the land, unarmed North Korean soldiers manned a barbed-wire border fence, chatting, laughing and sitting on their haunches while farmers ploughed the bare fields behind them.
Dandong, a bustling little city with a clutch of new high-rise apartment blocks lining the river, remained quiet.
In narrow, dusty streets surrounding Dandong's main customs office, traders loaded trucks with boxes of fruit and daily necessities ordered ahead of a national holiday celebrating the birthday of North Korean state founder Kim Il-sung.
"Is any country really scared of them?" said Chinese retiree Zheng Jia, 73, walking along the riverbank which faces North Korea. "China may back them, there's no way China will support them starting a fight."
China's Defence Ministry on Friday denied foreign reports that the People's Liberation Army was building up on the country's border with North Korea.
Still, state media said that another Chinese border city, Hunchun, had carried out an unusual air raid drill on Thursday, though images carried on Hong Kong's Phoenix Television suggested it was small scale, with old ladies shown shuffling into shelters clutching handkerchiefs over their mouths.
Rather than unsettling anyone, the reports caused some mirth on Sina Weibo, China's Twitter-like microblogging site.
"You're kidding," wrote one user. "I live in Hunchun and I heard nothing about this."